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Dynamically loading external files [message #485753]

Mon, 14 September 2009 19:51

Ric Wright

Messages: 70
Registered: July 2009

Member

I have written a (physics) modeling system that manages datasets, dataflow
and visualization dynamically. Third parties can write their own
data-processing and visualization classes and have them included in the
workflows. The external classes are loaded via reflection (i.e.
ClassForName and then classe.getConstructor(types).newInstance(args).

This all works fine as long as the class is within the jars that make up the
modeling system. But if the class is in some third party jar that the
modeling system has never seen before, then of course the classloader can't
find the class.

Is there a way to update the classpaths the classloader searches WITHOUT
recompiling or otherwise change the host modeling system?

TIA, Ric

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Re: Dynamically loading external files [message #485947 is a reply to message #485753]

Tue, 15 September 2009 15:48

Paul Webster

Messages: 6859
Registered: July 2009
Location: Ottawa

Senior Member

Are you talking about a java app? Then adding the 3rd party jars to the classpath is enough to make them visible to Class.forName(*).

Is this an RCP application?

If you are talking about turning your modeling engine into a plugin and then having other plugins contribute to it, then that's done via extension points and extensions.

Otherwise you have to use Buddy classloading (that's still 2 plugins).

If you are talking about having your modeling engine in a plugin and then loading extra classes from jars on the system ... well, that's another story entirely Smile

Paul Webster
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Re: Dynamically loading external files [message #485965 is a reply to message #485947]

Tue, 15 September 2009 17:51

Ric Wright

Messages: 70
Registered: July 2009

Member

Well, it is "another story entirely". The modeling engine is implemented as
a group of plugins that form a perspective. The engine needs to be able to
instantiate objects that are present in 3rd party jars that are not known to
the engine at compile time for the engine. The classes in the third party
jar implement interfaces or abstract classes that are defined in the engine.
All this works now as long as the "3rd party jar" is known to the engine
when the engine is compiled (so the classpaths are known). But that isn't a
palatable requirement down the road.

I have done a little spelunking and it looks like I can achieve what I want
either using URLLoader classloader or writing my own classloader. The
former may sandbox the class causing grief. I don't know a lot about
classloaders so I probably have some learning ahead. :-)

Thanks,
Ric

On 9/15/09 8:48 AM, in article h8od10$gnh$1@build.eclipse.org, "Paul
Webster" <pwebster@ca.ibm.com> wrote:

> Are you talking about a java app? Then adding the 3rd party jars to the
> classpath is enough to make them visible to Class.forName(*).
>
> Is this an RCP application?
>
> If you are talking about turning your modeling engine into a plugin and then
> having other plugins contribute to it, then that's done via extension points
> and extensions.
>
> Otherwise you have to use Buddy classloading (that's still 2 plugins).
>
> If you are talking about having your modeling engine in a plugin and then
> loading extra classes from jars on the system ... well, that's another story
> entirely :)
>
> PW

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Re: Dynamically loading external files [message #485991 is a reply to message #485965]

Tue, 15 September 2009 19:53

Eclipse User

Originally posted by: richkulp.us.NO_SPAM.ibm.com

Since your modeling engine was developed as a plugin, can you instead
require the "3rd party jars" to be plugins instead and they would use
extension points? That would simplify your whole problem. You would use
the extension points instead of looking up classes.

But if you require to also run outside of Eclipse plugins then you will
need to do classloader gunk.

--
Thanks,
Rich Kulp

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Re: Dynamically loading external files [message #486025 is a reply to message #485991]

Tue, 15 September 2009 23:15

Ric Wright

Messages: 70
Registered: July 2009

Member

Ah, that is an interesting idea. I was thinking more in terms of generic
Java. Requiring the third party jars to be plugins is eminently doable. I
have little experience of defining extension points - only implementing
them. More learning ahead. But that sounds better than learning more about
the black art of classloaders - about which I know only a little but more
than I want.

Thanks,
Ric

On 9/15/09 12:53 PM, in article h8orce$449$1@build.eclipse.org, "Rich Kulp"
<richkulp@us.NO_SPAM.ibm.com> wrote:

> Since your modeling engine was developed as a plugin, can you instead
> require the "3rd party jars" to be plugins instead and they would use
> extension points? That would simplify your whole problem. You would use
> the extension points instead of looking up classes.
>
> But if you require to also run outside of Eclipse plugins then you will
> need to do classloader gunk.

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Re: Dynamically loading external files [message #486133 is a reply to message #486025]

Wed, 16 September 2009 13:34

Eclipse User

Originally posted by: richkulp.us.NO_SPAM.ibm.com

Hi,

Here's an article on the plugin architecture including extensions.

http://www.eclipse.org/articles/Article-Plug-in-architecture /plugin_architecture.html

Ric Wright wrote:
> Ah, that is an interesting idea. I was thinking more in terms of generic
....
> them. More learning ahead. But that sounds better than learning more about
> the black art of classloaders - about which I know only a little but more
> than I want.
>
> Thanks,
> Ric

--
Thanks,
Rich Kulp

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Re: Dynamically loading external files [message #487043 is a reply to message #486133]

Mon, 21 September 2009 16:06

Ric Wright

Messages: 70
Registered: July 2009

Member

Thanks, Rich. That turned out to be good advice. It's all working smoothly
now.

Ric

On 9/16/09 6:34 AM, in article h8qph8$aif$1@build.eclipse.org, "Rich Kulp"
<richkulp@us.NO_SPAM.ibm.com> wrote:

> Hi,
>
> Here's an article on the plugin architecture including extensions.
>
> http://www.eclipse.org/articles/Article-Plug-in-architecture /plugin_architectu
> re.html
>
>
> Ric Wright wrote:
>> Ah, that is an interesting idea. I was thinking more in terms of generic
> ...
>
>> them. More learning ahead. But that sounds better than learning more about
>> the black art of classloaders - about which I know only a little but more
>> than I want.
>>
>> Thanks,
>> Ric

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Re: Dynamically loading external files [message #487067 is a reply to message #487043]

Mon, 21 September 2009 18:02

Eclipse User

Originally posted by: richkulp.us.NO_SPAM.ibm.com

Great!

Ric Wright wrote:
> Thanks, Rich. That turned out to be good advice. It's all working smoothly
> now.
>
> Ric
>

--
Thanks,
Rich Kulp

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